An antimagnetic watch is a timepiece that is able to resist magnetism. Magnetism is caused by the magnetic fields created by the electrical appliances that surrounds us daily.
The Four Fundamental Forces of Nature
As we understand today, our universe is governed by four fundamental forces of nature. They are, gravity, electromagnetic force, strong nuclear force and weak nuclear force. Science uses these four forces to explain everything around us. They explain how everything in the world is held to together and how everything interacts with each other. Gravity and electromagnetic forces operate at the atomic level and have an infinite range, meaning they can have an effect even at the distance between two planets. Strong and weak nuclear forces operate at a subatomic level, delving into the realm of quantum physics.
The Charged Particle
The basic and smallest building block of all matter in the universe is an atom. It consists of a nucleus of neutrons and protons surrounded by electrons. If an atom has an equal number of protons and electrons, it is in a neutral state. If an atom gains an electron from another atom, it becomes a negatively charged particle while an atom that loses an electron to another atom, becomes a positively charged particle. This can happen when two objects rub together.
When two charged particles interact, similar charges will repel each other while opposite charges will attract each other. For example, after a comb runs through hair, it leaves the hair positively charged, causing them to repel and stand up, while a balloon will stick to the wall due to opposite charges attraction. This push and pull interaction between two charged particles is known as the electric force. The electric force is always present between two charged particles, regardless if they are static or in motion. However, when these charged particles start moving, they create a magnetic field.
The Magnetic Field
Moving charged particles, like an electric current moving through a wire, creates a magnetic field around the wire. This was discovered by Hans Christian Oersted in 1820, when he observed a compass needle move when an electric current flowed through a wire. The magnetic field created will magnetize any magnetizable material that comes near it. Since electrical energy operates all around us, it creates overlapping magnetic fields, which can magnetize the micro parts in our watches, whenever we come into contact with it.
The materials used to make micro parts in our watches can mostly be categorized as ferromagnetic, paramagnetic or diamagnetic. Ferromagnetic materials like iron, nickel and cobalt exhibit magnetism at highly detectable levels. This means they can be easily magnetized and become temporary magnets themselves, even after the magnetic field is removed. Watches with such materials or steel combination alloys are the ones that get easily magnetized.
Paramagnetic materials like aluminum, platinum, titanium, manganese, chromium, molybdenum or combination alloys can get slightly magnetized but they don’t retain the magnetism after the magnetic field is removed. Diamagnetic materials are repelled by magnetic fields, they don’t get magnetized. Copper, silver, gold, zinc and the newer silicon, carbon combination alloys are diamagnetic. See The History of the Antimagnetic Watch Metallurgy.
Antimagnetic watches can be made of ferromagnetic materials shielded by paramagnetic soft-iron or totally made from diamagnetic materials. Thus, an antimagnetic watch is a timepiece that is able to prevent magnetic fields, from affecting its movement.
Standards
In order to be acknowledged as an antimagnetic watch, ISO 764, first established in 1973, requires the watch to keep its accuracy to ± 30 sec/day after being exposed to a direct current magnetic field of 4,800 A/m (Ampere per meter). The German DIN 8309, specifies the same minimum requirements and test methods for magnetic resistant watches. More recently in 2015, Omega, in partnership with The Swiss Federal Institute of Metrology (METAS), introduced the Master Chronometer certification, which requires both the watch and the movement, to maintain the mean daily accuracy (in various positions and at different temperatures) between 0 and +5 seconds/day, before and after exposure to magnetic fields in excess of 15,000 Gauss (approx. 1,200,000 A/m).
In comparison, typical household appliances like a computer has a magnetic field of 25 A/m while a microwave oven has about 150 A/m with motorized devices like hair dryers having up to 1,500 A/m. MRI machines at a hospital averages about 1,200,000 A/m and this value can go up 20-fold in scientific laboratory applications. So, rest assured that any watch that complies to ISO 764 or DIN 8309 is antimagnetic enough for daily needs.
Note: 4,800 A/m (SI unit) = approx. 60 G (Gauss) = approx. 6 mT (milliTesla).
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